Now that the cystic fibrosis (CF) gene has been identified (Rommens et al:, 1989), direct genetic testing for this disorder is available. However, about 30% of carriers cannot be easily detected with current technology. This lack of precision has generated a controversy concerning whether population screening is advisable (Wilfond and Fost, 1990). In contrast, there is general agreement at this time that testing for carders should be offered to CF-affected families. A study of CF siblings conducted prior to the discovery of the CF gene revealed significant distortions of genetic and medical information about the disease (Fanos, 1987). Further studies of testing and counseling in individuals from affected families can provide useful information with which to approach testing in the general public. We are in a position to evaluate four distinct groups of individuals from CF-affected families who have been offered carrier testing: tested and untested CF siblings, and tested and untested spouses of these individuals, to accomplish the following Specific Aims: 1. To Identify factors motivating or Interfering with the pursuit of CF carrier testing in siblings; 2. To assess CF sibling spouses' level of Interest In testing; 3. To assess levels of understanding of test results, medical aspects, and genetics of CF; 4. To assess psychological functioning of CF siblings and spouses following testing, to Identify problems to be addressed In testing programs. The sample consists of all adult CF siblings and spouses (total 102 individuals) who live in the Bay area and have had testing through our Medical Genetics center since 1989. We will also attempt to contact their CF siblings who have not had testing. All participants will be interviewed and standardized anxiety and depression scales will be administered. Qualitative material will be coded and reliability established by an independent rater. This is a 3-year project with an evaluation phase in the second year, and a potential for restructuring of the genetic testing and counseling format in the second and third year to improve service delivery.